Neuropathic pain: clinical classification and assessment in patients with pain due to cancer

Neuropathic cancer pain (NcP) is associated with worse treatment responses and specific therapy indications, but a standardized clinical diagnosis of NcP is still lacking. This is a prospective observational study on outpatients with cancer, comparing different clinical approaches with NcP evaluation. A three-step assessment of NcP was performed using DN4 (cutoff of 4), palliative care physician Clinical Impression, including etiology and pain syndrome identification, and Retrospective Clinical Classification by a board of specialists with the IASP Neuropathic Pain Special Interest Group criteria. Neuropathic cancer pain classification was specifically referred to pain directly due to cancer. Three hundred fifty patients were assessed, and NcP prevalence was 20% (95% confidence interval [CI] 15.9%-24.6%), 36.9%, (95% CI 31.6%-42.1%), and 28.6% (95% CI 23.8%-33.9%) according to DN4, Clinical Impression, and Retrospective Clinical Classification, respectively. Cohen's kappa concordance coefficient between DN4 and Retrospective Clinical Classification was 0.57 (95% CI 0.47-0.67), indicating moderate concordance. Higher percentages of discordance were found for specific pain syndromes such as pain due to deep soft tissue infiltration and pain associated with tenesmus. Disagreement among clinicians accounted also for different NcP diagnoses and highlighted lack of homogeneous clinical criteria. Rigorous application of etiological and syndrome diagnosis to explain pain cause, associated with standardized diagnostic criteria and assessment of pain characteristics, that is also specific for the cancer pain condition could improve clinical classification of NcP.